The invention has been developed to prevent or reduce several problems occurring in a hydrocarbon reservoir and its horizontal well(s) when subjected to production-related changes in the reservoir fluids. Among many things, these production-related changes lead to fluctuating production rates and uneven drainage of the reservoir. More particularly, this invention seeks to remedy problems associated with production-related changes in the viscosity of the reservoir fluids.
At the upstream side of a horizontal well the production tubing is placed in the horizontal or near-horizontal section of the well, hereinafter simply termed horizontal section. During production the reservoir fluids flow radially in through orifices or perforations in the production tubing. The production tubing also may be provided with filters or so-called sand screens that prevent formation particles from flowing into the production tubing.
When the reservoir fluids flow through the horizontal section of the production tubing, the fluids are subjected to a pressure loss due to flow friction, and the frictional pressure loss normally is non-linear and is increasing strongly in the downstream direction. As a result, the pressure profile in the fluid flow in the production tubing will is non-linear and is decreasing strongly in the downstream direction.
At the onset of production, however, the fluid pressure of the surrounding reservoir rock often is relatively homogenous, and it changes insubstantially along the horizontal section of the well. Thus the differential pressure between the fluid pressure of the reservoir rock and the fluid pressure inside the production tubing is non-linear and is increasing strongly in the downstream direction. This causes the radial inflow rate per unit length of horizontal section of the production tubing to be substantially larger at the downstream side (the “heal”) than that at the upstream side (the “toe”) of the horizontal section. Downstream reservoir zones therefore are drained substantially faster than upstream reservoir zones, causing uneven drainage of the reservoir.
During the early to intermediate stages of hydrocarbon recovery, and especially in crude oil recovery, this situation may cause water and/or gas to flow into downstream positions of the horizontal section and to mix with the desired fluid. This effect is referred to as so-called water coning or gas coning in the well. This particularly applies to wells having extensive horizontal length, the length of which may be in the order of several thousand meters, and in which the frictional pressure loss of the fluids within the horizontal section is substantial. This situation causes technical disadvantages and problems to the production.
Uneven rate of fluid inflow from different zones of the reservoir also cause fluid pressure differences between the reservoir zones. This may result in so-called cross flow or transverse flow of the reservoir fluids, a condition in which the fluids flow within and along an annulus between the outside of the production tubing and the wellbore wall in stead of flowing through the production tubing.
Due to said recovery related situations and problems, flow control devices may be used to appropriately choke the partial flows of reservoir fluids flowing radially into the production tubing along its horizontal inflow portion, and in such a way that the reservoir fluids obtain equal, or nearly equal, radial inflow rate per unit length of the well's horizontal section.